An Investigation of the use of a High Resolution ADC as a "Digital Biopotential Amplifier"

Sigma delta analogue to digital converters have been used in many signal processing applications including some commercially available systems for sampling of biosignals [1], [2]. Bio-potential amplifiers have traditionally utilised specialised high-quality analogue components to amplify bio-signals. The central aim of this work is to investigate the benefits of using high-resolution sigma delta conversion as a digital amplification stage in the signal path of a bio-potential amplifier. A number of system arrangements specific to bio-potential measurement are presented and discussed. These arrangements are designed to use the high-resolution capacity of the sigma delta converter in different ways, providing different benefits. To explore these benefits, the authors have implemented a digital bio-potential signal capture system consisting of a sigma delta converter interfaced to a PC running MATLAB via an inexpensive microcontroller and to test it with a number of test signals. A signal generator which simulates the attributes of an Electrocardiogram was used together with analogue signal conditioning for two electrode and three electrode measurement to provide suitable signal sources for capture using the digital bio-amplifier. The results were analysed to investigate the trade off between signal resolution and analogue amplification.